In the screen capture attached, you can read the 'heading 1' style, but the 'heading 2' and 'heading 3' style previews are unreadably small. (You'll also notice that the 'box' is pretty small too)
I have to think that this is a bug of some kind - both of those headings are using a background stroke decoration, set to twice the height of the font. I wonder if that might be the problem area here (see second screenshot)